The induction of tolerance in transplantation and autoimmunity remains an elusive clinical goal. A more thorough understanding of the fundamental mechanisms of immunologic tolerance is therefore necessary. We propose here a multidisciplinary approach to investigate peripheral mechanisms of immunologic tolerance by studying murine models of solid organ transplantation, bone marrow transplantation, and autoimmunity. A multidisciplinary approach is proposed because the mechanisms responsible for tolerance to self and foreign antigens overlap, and because significant cross-talk among the three clinical disciplines exists: bone marrow transplantation is increasingly employed to induce tolerance to solid organ allografts, and therapeutic agents used in transplantation are applicable to patients with autoimmunity (and vice versa). [unreadable] The PPG consists of three integrated projects and a core: histopathology. Integration among the projects is based on commonality of immunologic concepts, ongoing and future collaborations between the investigators, and the sharing of methods and resources. Project 1 will explore the mechanisms of dendritic cell maturation that lead to graft-versus-host disease (GVHD) following bone marrow transplantation. Project 2 will investigate tolerance induction via the generation of regulatory T cells (Treg) in a mouse model of inflammatory bowel disease. Project 3 will explore the phenomenon of immunologic ignorance by studying the innate and adaptive mechanisms that are responsible for continued recognition of a transplanted organ by the host's immune system. The Histopathology Core will provide tissue processing, staining, immunohistochemistry, in situ hybridization, imaging, and interpretation services to all three projects.